The famine did not affect all of Ireland in the same way. Suffering was most
pronounced in western Ireland, particularly Connaught, and in the west of Munster.
Leinster and especially Ulster escaped more lightly. The following map shows the severity
of the famine across Ireland in 1847; the height of the Famine.

There are a number of reasons for this pattern:

As discussed in Prelude to Famine 1: Irish Agriculture,
there were several distinct kinds of agriculture present in Ireland at the time of the
famine. The farmers in the east depended upon cereal crops, while those in Ulster grew
flax. Only in the small farms of west of Ireland, and in parts of Munster, was the potato
in a monopolistic position. It is estimated that at the eve of the famine 30% of Irish
people were largely or wholly dependant on potatoes for their food. Thus, when the Blight
struck it was these people who had nothing to fall back on. In Connaught some have
estimated that as many as 25% of the population died.

Those who lived nearer to large cities had more access to imported goods. Although food
was exported as usual from Leinster in 1844 and 1845, there was a net import of almost a
million tons of grain by 1847. However, these imports naturally reached those nearer to
the cities and these are in the east and south. Dublin, Belfast and Derry escaped with
almost no effects at all, while Cork and Wexford were relatively better off than their
rural environs. It was the inland and especially the western areas that could benefit
least from the food of the cities. Given the fact that potatoes are notoriously hard to
transport in any case, it would be difficult to get potatoes to Connaught even in a
non-famine situation.

More people were killed by malnutrition-related diseases (such as dysentry and scurvy)
as well as cholera that swept through the famine-ravaged countryside, than by actual
starvation. While already prevalent in the west, many of these diseases spreads most
effectively in damp conditions where people live closely together. Dysentry is not caused
by hunger, and its incidence was not significantly higher during the famine as before.
However, recovery from Dysentry depends upon good nutrition and in many cases this was
unavailable. The Cholera epidemic was coindicental to the famine, but was responsible for
a large number of deaths. It was the closely packed west that suffered most from these
effects.

Note: While this explains the pattern of suffering, the reasons for the severity
of the suffering is an entirely different issue. See later chapters.